The invention relates to improvements in electrically operated portable hair dryers of the type wherein a housing confines an electric motor which drives a rotary impeller serving to induce a flow of air through an electric heating unit and thereupon to the outlet of the housing.
A hair dryer of the above outlined type normally further comprises a lattice or filter at the inlet of the housing so that the inflowing air passes through the interstices of the filter on its way into the range of the impeller, and a grate at the outlet of the housing. Furthermore, it is customary to provide the hair dryer with a system of guide vanes or analogous air guiding elements which guide the air between the impeller and the heating unit.
The grate at the outlet of the housing normally comprises a set of concentric cylindrical walls which are connected to each other by webs to define apertures for the flow of heated air to the outlet of the housing. The common axis of the walls coincides with the longitudinal axis of the housing of the hair dryer. A drawback of such grates is that they do not ensure a sufficiently uniform distribution of heated air which issues from the housing of the hair dryer. The reason is that, when one considers the combined area of apertures in the grate, the speed of outflowing hot air in certain portions of such combined area is higher than in other portions. This is undesirable because the user or operator of the hair dryer is not in a position to treat the hair in a predictable manner.
The air guiding elements or vanes (which jointly form a so-called guide wheel or diffuser) of conventional hair dryers are normally aligned (in register) with the customary carriers of one or more electric heating elements. The arrangement is normally such that the strip- or plate-like carriers of the heating element or elements extend radially outwardly from and in parallelism with the axis of rotation of the impeller downstream of stationary guide vanes of the guide wheel. The carriers form a substantially star-shaped array and are normally equidistant from each other; the heating element or elements are disposed at the outer sides of such carriers. Each carrier is in register with a guide vane. The reason for such positioning of carriers and vanes in common planes which are parallel to the axis of rotation of the impeller is that this is believed to entail a reduction of the resistance which the carriers and the guide vanes offer to the flow of air toward and along the heating element or elements. It has been found that, though the just described positioning of guide vanes and carriers relative to each other might reduce the resistance which is offered to the flow of air through the guide means and into the range of the heating unit, the heating unit is likely to unduly increase the temperature of air so that the heated air can damage or even destroy the housing of the hair dryer.